Method of producing refined metals and alloys.



A. E. GREENE.

METHOD OF PRODUCING REFI-NED METALS AND ALLOYS.

APPLICATION FILED JULY 22, 1908.

1,034,785. Patented Aug". 6, 1912 fnz/ezzz or SMQQMEBMQZA YerZZ. Green/e mwwww UNITED STATES PATENT 0mm f ALBERT E. GREENE, OF CHICAGO, ILLINOIS, ASSIGNOR T0 AMERICAN ELECTRIC SMELTING AND ENGINEERING COMPANY, OF ST. LOUIS, MISSOURI, A CORPORATION" OF MISSOURI,

METIIOD OI PRODUCING REFINE!) METALS AND ALLOYS;

To all whom it may concern:

Be it known that I, ALBERT E. GREENE, a citizen of the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Methods of Producing Refined Metals and Alloys, of which the following is a full, clear, concise, and exact description.

My'invention relates to a process of refining or otherwise treating metals or alloys of metals.

More specifically it relates to a process by which sulfur and phosphorus, or either of said elements may be eliminated or separated from the mixture of elements, thereby leaving the remaining constituent or constituents ofthe mixture in a refined condition.

In metal refining processes based upon the oxidation of the impurity to be eliminated, the refining of the metal is usually accompanied by a greater or less oxidation of the metal itself. Such undesired oxida tion of the metal results in a partial loss of the metal and is also an actual hindrance to the practice of the process, since the presence of the metallic oxid in the slag interferes with the removal of certain impurities, such as sulfur, which would otherwise be taken up by the slag. In the I-Ieroult steel process designed to overcome these objections the removal of phosphorus from the bath is likewise accompanied by the presence of iron oxid in the slag, but such iron oxid may be deoxidized by means of calcium carbid formed from the lime slag employed. After the elimination of phosphorus and the deoxidation of the iron oxid the sulfur in the bath may be removed by a separate washing process with a lime slag.

My invention contemplates the formation of a compound of the elements to be eliminated from the material under treatment, without any attendant formation of undesired compounds of the elements to be retained.

My invention contemplates, in the more Specification 01 Letters Patent.

Application filed July 22, 1908. Serial No. 444,740.

Patented Au 6, 1.912.

usual detrimental oxidation of the metal itself or other elements which it is desired to retain.

In certain cases my invention contemplates dispensing with the usual slag-forming flu x, as, for example, where the oxidized impurity passes off in the form of gas, or where the temperature of the bath is such that the oxidized impurity is not susceptible to subsequent reduction by the metal of the bath.

In certain other cases my invention contemplates the use of a slag-forming flux for removing the'oxidizedphosphorus and also for simultaneously removing sulfur from the bath.

One feature of my invention consists in a combined regulation of the temperature of the material which is under treatment and of the pressure of dissociation of the treating agent employed. In case the treating agent is oxygen or an oxygen compound, this feature of the invention consists in the combined regulation of the temperature of the material under treatment andof the oxygen pressure of" the oxidizing agent which is added to or, where a gaseous agent is employed, which is forced into contact with the treated material. More specifically, this latter feature. of my invention consists in maintaining the temperature of a metallic bath at a point where the oxygen pressure of the oxid of phosphorus is below the oxygen pressure of any oxid which is capable of being formed from the metal or metals to be retained in the bath, and, under such temperature conditions, introducing into the bath an oxidizing agent whose oxygen pressure is above that of the oxid of the substance to be eliminated but below that of the oxid which would result from the combination of oxygen with the metal or metals to be retained in the bath. In other words, the treating agent has an oxygen pressure which causes it to act as an oxidizing agent for the element or elements which it is desired to eliminate from the bath but which causes it to act as a reducing agent for the oxide of such element or elements as it is desired to retain in the bath.

Another feature of my invention applicable. to particular'conditions consists in a combined regulation of the temperature of the materials under treatment and of the pressure, within the furnace chamber, of the gases resulting from the reaction, thus so controlling the pressure of dissociation of the materials under treatment and of the products resulting from the t-reatment'as to produce conditions favorable to the elimination of an undesired element from the material under treatment.

These and other features of my invention may be more readily understood by reference to the accompanying drawings, in whichv Figurel is a plan view of an electric refining furnace which represents one type of furnace in connection with which the processof my invention may be practised; Fig. 2 is a sectional view on the line 2-2 of Fig. 1; Fig. 3 is a sectional view on the line 3-3 of Fig. l; and Fig. 4 is a diagram showing.

the characteristic curves of oxygen pressure for the oxids of two elements, for example, iron and phosphorus, as they lie relatively to each other at different temperatures.

I have discovered that in the case ofcertain elements, each susceptible to oxidation, either of them may serve as a reducing agent for the oxid of the other, according to the temperatures maintained. This is due to the fact that the relative, as well as the- For example, at a given temperature silicon may have such a relatively high aflinity for oxygen as to serve as a reducing agent for iron oxid, whereas at a different temperature the reverse may be true, the metallic iron then serving as a reducing agent for the oxid of silicon. I

I have discovered that by suitably regulating the temperature of a mixture or compound containing two elements having the above-desbribed characteristics, and by subjecting the mixture or compound to the action of an oxidizing agent whose oxygen pressure is between the two oxygen pressures corresponding to the oxygen pressure of the oxids of the elements of the mixture or compound, I can thereby oxidize that .element having the lower oxygen pressure without oxidizing the element having the higher oxygen pressure. This method of tomes oxidizing one element of a mixture without,

the oxidation of any other element or elements thereof is based upon the above-mentioned facts relative to the pressure of dissociation of oxids or, in other words, to the oxygen pressure of oxids.

From the foregoing it appears that for every temperature there is a definite oxygen pressure for any given oxid below which pressure the oxid cannot form from its elements. It further follows that the series of points representing the oxygen pressures of a given oxid for difi'erent tem erat-ures form a curve, which curve is di erent for different elements.' Within the working range of furnace temperatures, these curves for certain pairs of elements may even cross each .other. At the point of intersection of the two curves the relative aiiinities of the two elements for oxygen tare reversed. The

.peraturecorresponding to the point of inter section a of the two curves, that is, at the critical temperature of iron and phosphorus with respect to each other, which critical temperature is above 1700 0., the oxygen pressures FeO and P 0 are equal, and the two elements, iron and phosphorus, have an equal afinity for oxygen. At any temperature lower than the critical temperature, the oxygen pressure of FeO is greater than the oxygen pressure of P 0 Hence if an oxidizing agent having itself an oxygen pressure intermediate to those of FeO and P 0 be introduced into a mixture of iron and phosphorus, such oxidizing agent will act as a carrier of oxygen to the element having the lower oxygen pressure, butnot for the element having the higher oxygen pressure.

The oxygen pressure at any given temperature of any given oxidizing agent, may readily be ascertained. In the case of a gaseous agent, or an agent which may assume a gaseous state, the pressure of dissociation thereof is dependent onboth the temperature and the pressure or degree of compression of the gas. The eifect of pressure on a gas giving oxygen by dissociation,

as, for example, GO :CO+O,

is the opposite to that due to temperature,

the former lowering and the latter raising the oxygen pressure of the gas. The pressure of oxygen in a gas may be further regulated by mixing with the gas another gas, as for instance a gas having a different oxygen pressure. The amount of the different constituents of the mixed gas and the degree of pressure of the gaseous mixture may be regulated to obtain the best results at the temperature at which it is desirable to practice the process.

The oxygen pressure of air is the actual pressure due to the oxygen constituent thereof and is approximately mesa}; of an atmosphere. The oxygen pressure 0 carbon dioxid (CO is the actual partial pressure of the available oxygen at the working temperature, and is much lower than that of air. The oxygen pressure of carbon monoxid (CO) under atmospheric pressure is exceedingly low. In case a gaseous oxidizing agent is desired having an oxygen pressure greater than that of carbon dioxid, such agent may be obtained by mixing air and carbon dioxid and properly regulating the relative amounts of each, and a gaseous mixture may thus be obtained having any desired oxygen pressure between that of air as a maximum and that of carbon dioxid as a minimum. Other gases, one at least of which contains oxygen, may be mixed so as to give the desired result.

The oxygen pressure of a gaseous compound, it will be understood, is the actual pressure of the uncombined oxygen and of the oxygen made available by the disassociation of oxygen compounds. gen thus available for forming new combinations is a definite proportion of the entire volume of the gas, and hence the oxygenpressure is a definite percentage of the entire working pressure of the gas. The method of calculating oxygen pressure .is well known and forms. no part of my present invention. In a general way, to ascertain the percentage of this available oxygen, I employ tables similar to those disclosed in Nernsts Theoretical Chemistry, 4th edition, (1904:) pages 44:44:45.

The method which I preferably employ for obtaining a gaseous agent having the de sired oxygen pressure consists as above set" forth in properly mixing two or more gases one at least'of which contains oxygen. The

mixing is preferably done by blowing each gas from a separate engine or compressor into a common receiver or pipe and regulating the speed of each unit to furnish the desired amount of each gaseous constituent of the mixture. Such apparatus is shown in .the drawings, in which the blowers 1, 2 communicate with a common receiver or pipe 3.

The process of my invention may be practised with the usual well-lmown types of furnaces, heated in any desired manner, as for example, by that type of furnace in The total oXy-.

quired temperature of the mixture under treatment. I prefer, however, to use an electric furnace in general similar to the well-known Heroult tilting furnace. Such furnace is shown in the drawings, and consists of a crucible 4 closed by a cover 5 provided with a chimney 6. The electrodes 7, 7 pass through the cover 5. The furnace is provided with a spout 8 for running off the metal on tilting the furnace. The furnace may be provided with a charging opening closed by a door 9. The electrodes may consist of the usual carbon electrodes. The furnace is provided above the base of the crucible with openings for receiving twyers 10, which communicate in the usual way with the pipe 3. The. twyers preferably dip down into the molten bath 11.

Any suitable source of electric current may be employed, the connections of the electrodes in the circuit being made in a manner well understood by those skilled in the art.

In order to more clearly set forth my invention, I will describe in detail one of'the applications of my process, and for that purpose will describe the operation for the removal of phosphorus and sulfur from steel.

Molten metal containing phosphorus and sulfur which m ght come, for example, from an acid converter is charged into the furnace through the charging opening. The temperature of the bath is regulated by regulating the flow of the electric current to the proper, point for the most efficient elimination of phosphorus without appreciable oxidation of the iron of the bath. In general, it is desirable that this temperature be as far from the critical temperature of phosphorus and iron as is practicable in order to obviate the'possibility of detrimental oxidation of the iron.

A basic lime flux 12 is" preferably melted on top of the bath 11. This slag'is preferably basic enough to take up the phosphorus and sulfur, but not more so than is necessary, in order that the electric energy required to melt it'may be as small as possible. Gas of proper oxygen pressure for selectively oxidizing the phosphorus without oxidizing the iron is supplied from the pipe 3, and is blown through theitwyers 10 into contact with the bath 11. This causes an oxidation of the phosphorus into phosphoric oxid, P 0 which is taken up by the basic slag. Since the oxidizing gas causes no oxidation of the iron, the absence of iron oxid in the slag permits of the slag also serving to eliminate the sulfur. 1

By practising the process as thus de scribed, the metal cannot be overblown if the proper'conditions are maintained. In

some cases, however, it may be desirable from a commercial standpoint to lessen the time required for practising the process at the expense of a slight loss of iron. Hence I do not wish to be understood as limiting my process to conditions under which the oxidation of the iron is entirely prevented. It suilices if the conditions are such that no detrimental oxidation of the iron takes place. If the oxidation of the iron is so small as not to seriously interfere with the removal of other impurities, such practice of the process is within the scope of this invention. The oxidizing action is continued until a test sample of the material under treatment shows that the metal has been sufiiciently refined. The slag and metal may then be separated in the usual manner.

in practice I may employ as the oxidizing agent carbon dioxid mixed with air, the oxygen pressure of such mixture being regulated with respect to the oxygen pressure of Fe@ and P 0 in the manner hereinbefore described, that is by adding to the mixture of carbon dioxid and air a gas, such as carbon monoxid, that will render the mixture an oxidizing agent for phosphorus and at the same time a reducing agent for the oxids of iron at the temperature at which the materialunder treatment is maintained. The CO gas may be obtained from any desired source practice I have found that satisfactory results may be attained by employing the stack gases from blast furnaces and modifying such gases, as may be necessary,,to provide the required oxygen pressure of the gaseous treating agent.

By properly regulating the oxygen pres sure of the gaseous mixture-employed, the oxygen available for oxidizing purposes is used up in oxidizing the element eliminated from the bath. Hence, the resultant gas coming from the reaction constitutes a mom oxidizing or even a reducing atmosphere in the refining chamber, the CO gas being reduced by the reaction to C0 gas. This nonoxidizing or reducing atmosphere in the chamber containing the carbon electrodes is effective in protecting them from otherwise rapid. oxidation and also in' protecting the molten metal. g

The use of a lime flux as above setforth is preferable, for the reason that with a flux'to take up the oxidized. phosphorus it is possible to work nearer to the critical temperature of phosphorus and iron and also for the reason that the lime flux will at the same or oxygen.

aoaaaae which the deoxidizingagent calcium carbid is expenslve in time, material and electric energy. g

. The effect of the pressure in the furnace chamber of the gaseous body liberated therein tends to retard the action taking place in the body of the material. As a rule, owing to the tree escape of the gases through the chimney of the furnace, such pressure or the gases resulting from the reaction, is negligible. However, incertain cases the process may be advantageously expedited by reducmg the pressure in the furnace chamber. I may, therefore, employ a suction fan 12, as shown in Fig. 3, for removing through the chimney or escape vent 6 of the furnace the gases as they are formed, thus maintaining the atmosphere within the chamber under a reduced pressure more favorable to the practice of the process.

With reference to the practice of my process in general, it is to be understood that it is not limited to any particular method of regulating the temperature of the substance under treatment, or of subjecting the same to a suitable treating agent. Nor is it limited to any particular method of producing the desired pressure of dissociation of the agent employed. In many cases a gaseous agent already having the desired oxygen pressure may be available, as, for example, the gases emanating from the stack of an iron producing furnace, or such gases may be modified in a manner to give the desired oxygen pressure.

The critical temperatures of some of the metals with respect to other oxidizable elements-with which they are commonly associated are known. However, in case such temperature-for any required metal or met- 195 1. als is not known, a suitable working temperature can readily be ascertained by blowing 'samples'of the material to be treated at successively progressing temperatures with air By comparing the relative oxi- 11o dation of the different elements of such treated samples a temperature can be determined at which the element or elements to be eliminated from the metal have a stron er affinity for oxygen than has the metal whlch 115 it is desired to retain unoxidized. Having thus or in any other manner ascertained a suitable working temperature, a' gaseous mixture having oxidizing properties with respect to the substances to be eliminated 120 from the metal and having non-oxidizing properties with respect to the metal itself can readily be determined. A suitable gaseous mixture can best be selected by mixing with a reducing gas, as for example carbon 125 monoxid (CO), a gas having oxidizing pro erties, as for example carbon dioxid (C8 and treating -samples of the material to be refined, maintained at the working temperature previously ascertained in the 130 treatment should be thorough and should be prolonged beyond the point at which the undesired elements are eliminated from the metal. From among "those ofthe gaseous mixtures which do not oxidize, even with prolonged treatment at the selected temper-' ature, the metal which it is to retain unoxidized, a mixture should be selected which oxidizes the undesired components of the material, and preferably that mixture having the strongest oxidizing action at the selected temperature on said undesired components. In such manner a suitable working temperature and a gaseous mixture suitable for treating the material at such temperature can readily be ascertained.

My invention as applied to the removal of phosphorus may be further illustrated by a concrete example of the character of the material under treatment, the temperature at which it is maintained, and a gaseous mixture that will provide a suitable oxygen pressure at such temperature. With a charge consisting of Bessemer steel and a,

lime flux, maintained at a temperature of approxlmately 1700 (l, a gaseous mixture containing 23% of carbon monoxid (CO),

12% of carbon dioxid (CO and 1% of oxygen (0) will atapproximately atmospheric pressure, satisfactorily eliminate phosphorus and sulfur without danger of overblowing the iron. Such a gas at a temperature of 1700 0., will have an oxygen pressure of approximately 38 mm. of mercury. By actual test, under the above conditions, I have reduced phosphorus in Bessemer steel from 096%, to 019%, and sul fur from 041% to 013%, without oxidizing the iron. It will be understood that the above is but an example of one of the many gaseous mixtures that will according to my process accomplish the desired result. Forexample, though I have found that carbon dioxid alone Will oxidize iron at a temperature of 1300 (3., a mixture containing 12% of carbon dioxid and 3% of carbon monoxid will keep the iron reduced. I have furthermore used a mixture containing from 6 to 8% of carbon monoxid and from 12 to 15% of carbon dioxid and found that with the bath maintained at a temperature of about 1350 (l, the reducing agent carbon monoxid was present in suflicient quantity to prevent the oxidization of iron or manganese and yet that the mixture was oxidizing with respect to phosphorus. In the examples given the percentages are stated in volumes and the remaining portion of the mixture may consist of some inert gas, such as nitrogen.

It is apparent that the process broadly is applicable not only to the removal of phosphorus and sulfur, but also to the removal of other elements. Such broad features of m invention and certain other specific embodlments thereof are described in my co-pend-l ing applications, Serial No. 470,921 filed Jan. 6, 1909, Serial No. 488,360 filed Apr. 7, 1909, and Serial No. 531,529 filed Dec. 6, 1909.

I claim Y 1. The process of refining metals and alloys contalning phosphorus as an impurity, which consists in heating the material under treatment to a temperature at which the oxygen aflinity of phosphorus is greater than that of the element or elements to .be retained, and in subjecting the heated material to the action of a gaseous mixture containing an oxygen-compound having a pressure of dissociation suitable, at a temperature of the heated material, for oxidizing phosphorus but unsuitable for like action upon the element or elements which it is desired to retain unoxidized.

2. The process of refining metals and alloys contai'ningphosphorus as an impurity, which consists in heating the material under treatment, in the presence of a flux suitable for forming a slag with oxidized phosphorus, to a temperature at which the oxygen-affinity of phosphorus is greater than that of the element or elements to be retained, and in subjecting the heated mate'- rial to the action of a gaseous mixture containing an oxygencompound suitable, at the temperature'of the heated material, for oxidizing phosphorus but unsuitable or like action upon the element or elements which it is desired to retain unoxidized.

3. The process of refining metals and alloys containing phosphorus and sulfur as impurities which consists in heating the material under treatment, in the presence of a flux suitable for forming a slag with phosphorus and sulfur, to a temperature at which the oxygen-aflinity of phosphorus is greater than that of the element or elements to be retained, and in subjecting the heated material to the action of a gas containingcarbon dioxid mixed with carbon monoxid in proportions suitable for oxidizing phosphorus but unsuitable for a like action u on the element or elements which it is deslred to retain unoxidized.

4:. The process of purifying phosphorusbearing iron, which consist-s in maintaining, in a furnace, a molten bath of the material under treatment at a temperature at which the oxygen pressure of oxid of iron is higher than the oxygen pressure of oxid of phosphorus, and in subjecting the molten bath to a gaseous oxidizing agent having an oxygen pressure intermediate said aforenamed oxygen pressures.

5. The process of producing steel from an iron alloy containing phosphorus, which consists in maintainlng in a furnace a 'iron alloy containing phosphorus, which consists in maintaimng, in a furnace, a

p 1 molten bath of the alloy at a temperature at which the oxygen pressure of oxid of iron is higher than the oxygen pressure of oxidfof phosphorus and in subjecting the molten bath, in the presence of a flux, suitable {for forming a sla with oxidized phosphorus, to a gaseous oxi iz-i'ng agent havlngan oxygen pressure intermediate said aforenamed oxygen BEGSSUJQS.

'i he process of refining an iron alloy containing phosphorus and sulfur as impurities, which consists in maintaining in a furnace a molten bath of the mixture at a temperature at which the oxygen pressure of oxid of iron is higher than the oxygen pres sure of oxid of phosphorus, and in subjecting the molten bath to a gaseous oxidizing agent havi an oxygen pressure suitable for'the selectlve oxidation of the phosphorus of the bath.

8. The process of refining an iron alloy containing phosphorus and sul-furas impurities, which consists in maintaining in a furnace a molten bath of the mixture at a temperature at which the oxygen pressure of oxid of iron is higher than, the oxygen pressure of oxid of phosphorus, and n subjecting the molten bath to a gaseous oxidizing agent having an oxygen pressure intermediate saidaforenamed oxygen pressures.

9'. The process of refining an iron alloy containing phosphorus and sulfur as impurities, which consists in maintaining in a furnace a molten bath of the mixture at a temperature at which the oxygen pressure of oxid of iron is higher than the oxygen pres sure of oxid of' phosphorus, melting with the bath a flux high in lime, and in subjecting the molten bath to a gaseous oxidizing agent having an oxy en pressure suitable for the iel'ective oxidation of the phosphorus of the ath.

It). The process ofrefining an iron alloy containing'phosphorus and sulfur as impurities, which consists in maintaining in a furnace a molten bath of the mixture at a temperature at which the oxygen pressure of oxid' of iron is higher than the oxygen pres-- sure of oxid of phos horus at that temperature, melting with t e bath aflu-x suitable metered andalso suitable for taking up sulfur from ;the bath, and in subjecting the molten bath to a gaseous oxidizing agent having an oxyggen pressure suitable for the selective oxidajtion of the phosphorus-of the bath.

j 11. The process of refining metalsand algloys containing an impurity which when- ;oxidized is capable of forming a slagwith a fluxing agent, said process consisting in maintaining the material under treatment .1 at a temperature at which-- theoxygen pressure of the oxid of the element which is tosure of the oxid of the impurity, and in subj'ecting the material, in the presence of the flux suitable for forming a slag with the oxidized impurity, to a gaseous oxidizing agent having an oxygen pressure intermediate the said aforenamed oxygen pressures.

12. The process of refining metals and alloys, containing an impurity which when oxidized is capable of forming a slag with a fl'ux'lng agent, said process consisting in maintaining, in a furnace, a molten bath of the metal or alloy at a temperature at which the oxygen pressure of the oxid of the metal is higher than the oxygen pressure of the oxid of the impurity, and in subjecting the molten bath, in the presence of a flux suit able for forming a slag with the oxidized impurity, to a gaseous agent having oxidizing properties with respect to said lmpurity and reducing properties with respect to oxids of the metal.

13. The process of refining metals and alloys, containing an impurity which when fluxing agent, said process consisting in heating the material under treatment, in the presence of a flux suitable for forming a slag with the oxidized impurity, to a temperature at which the oxygen-afiinity of said impurity is greater than the oxygen-aiiinity of the element or elements to be retained, and in subjecting the heated material to the action of a gas containing carbon dioxid mixed with carbon monoxid in proportions such that the gaseous mixture has, at the temperatures of treatment, oxidizing properties with respectto said impurity and reducing properties with respect to oxids of such element or elements to be retained.

In witness whereof, I hereunto subscribe my name this twentieth day of July A. 1)., 1908. I

ALBERT E. GREENE. Witnesses:

CLARA P. CLARK, CATHERINE MORGAN.

; for forming a slag with oxidized phosphorus I be retained is higher than the oxygen presoxidized is capable-of forming a slag with a i 

